Get the diagonal without calculating the explicit matrix
1 回表示 (過去 30 日間)
古いコメントを表示
Dear all:
I am trying to calculate a diagonal of a matrix (denoted A), which is formed by multiplying two large-dimensional matrices (denoted as B*C).
A naive way to do it is: first, calculating explicitly A = B*C, then get diagonal out from A. However, the first step takes forever to run due to the high-dimension of B and C. But the only thing I need is the diagonal of A.
Another straightforward way in my mind is: I could create a loop by calculating each element of the diagonal of A one by one. It will surely save a lot of time, but I am not sure if this is the most efficient way.
I am wondering if anyone knows a faster/smarter way to calculate it.
Thank you very much in advance!
Best,
Long
1 件のコメント
採用された回答
その他の回答 (1 件)
the cyclist
2020 年 3 月 26 日
Here is one way:
% Make up some inputs
N = 4;
B = rand(N);
C = rand(N);
% Calculate the diagonal
A_diag = 0;
for nr = 1:N
A_diag = A_diag + B(:,nr).*C(nr,:)';
end
参考
カテゴリ
Help Center および File Exchange で Operating on Diagonal Matrices についてさらに検索
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!